First you need to register and log in. Click on the content board that you'd like to add content to, and then press the green Add a photo button . From there follow the instructions on screen. If you cant see the green button then you are not entitled to upload to that particular board. Some content boards may be for staff only uploads or entries may have been switched off as the finish date is reached.
To check out the full user process see this learning video - https://www.youtube.com/watch?v=pRPzOWmKvdI&list=PLRNxWZk7MeRpQpOa2w_TNfMS_YBi6etwa&index=1